Zothecula writes: Rocket engines are generally not thought of as being environmentally-friendly, but thanks to a newly-developed process, we may someday see them neutralizing the emissions from wastewater treatment plants. The same process would also see those plants generating their own power, thus meaning they would be both energy-neutral and emissions-free. Developed by two engineers at Stanford University, the system starts with the formation of nitrous oxide (N2O) and methane gas — something that treatment plants traditionally try to avoid.